Transmission upshift input torque modulation for a hybrid electric vehicle

ABSTRACT

In a powertrain for motor vehicle that includes an engine, an electric machine able to function alternately as a motor and a generator, and a transmission whose input is driveably connected to the engine and the electric machine, a method for controlling transmission input torque during an upshift including using the engine to produce torque transmitted to the transmission input, during the ratio change phase of the upshift, operating the electric machine as a generator, and during the ratio change phase of the upshift, controlling a net torque transmitted to the transmission input by using the engine to drive the transmission and the electric machine concurrently.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a powertrain for a hybrid electricvehicle (HEV), and, in particular to a method for performingtransmission input torque modulation during a change to a higher gear.

2. Description of the Prior Art

In a conventional vehicle equipped with a transmission that producesstep changes among gear ratios, the driver can experience drivelinedisturbances during a gear shift. The driveline disturbances occur dueto the acceleration and deceleration of the engine and transmissioncomponent inertias, which produce an inertial torque during the gearshift. In the case of an upshift, the transmission output torqueincreases during the ratio change phase of the gear shift as a result ofthe engine speed changing.

This output torque disturbance is directly felt by occupants of thevehicle and affects shift quality. The level of output shaft torquedisturbance increases with the speed of the upshift since enginedeceleration is greater with faster gear shifts. By reducing enginetorque produced during the upshift, inertial torque can be offset andthe output shaft torque increase can be minimized, thereby improvingshift quality. The method of reducing engine torque produced during theupshift is referred to as “input torque modulation” control.

In the case of a downshift, the transmission output torque decreasesduring the ratio change phase as the engine and transmission componentsaccelerate to the synchronous speed for the lower gear. Moreover, duringthe torque transfer phase of the downshift, the transmission outputtorque can spike near the completion of the downshift as the engineaccelerates. The drop in output torque during the ratio change isdirectly felt by the vehicle occupants and can give the sense of anacceleration discontinuity as the downshift is performed. The outputtorque spike at the end of the downshift can affect shift quality andproduce a feeling of a rough shift. Furthermore, the level of outputshaft torque drop and spike near the end of the downshift will increasein proportion to speed of the downshift.

By using input torque modulation, the engine combustion torque can bereduced near the end of the downshift in order to reduce the engine'sacceleration as the shift ends. As a result, the transmission outputtorque spike can be minimized and avoided, thereby reducing the shiftdisturbance.

In conventional vehicle applications, limitations and problems withinput torque modulation during gear shifts include limited engine torquereduction authority due to constraints, such as emissions; delayedengine torque response to torque modulation requests, further degradingshift quality; and poor fuel efficiency, since spark retardation iscommonly used for achieving torque modulation requests.

SUMMARY OF THE INVENTION

In a powertrain for motor vehicle that includes an engine, an electricmachine able to function alternately as a motor and a generator, and atransmission whose input is driveably connected to the engine and theelectric machine, a method for controlling transmission input torqueduring an upshift including using the engine to produce torquetransmitted to the transmission input, during the ratio change phase ofthe upshift, operating the electric machine as a generator, and duringan ratio change phase of the upshift, controlling a net torquetransmitted to the transmission input by using the engine to drive thetransmission and the electric machine concurrently. The engine torqueand torque required to drive the electric machine can be varied duringthe ratio change phase.

During a transmission shift event, the electric machine is controlled toproduce accurately a transmission input torque modulation request. Bytaking advantage of the electric machine's capability, output shafttorque disturbances are reduced and optimum shift quality is achieved.

The transmission input torque modulation control strategy can be appliedto HEV powertrains including rear wheel drive, front wheel drive and allwheel drive configurations, full HEV, mild HEV having at least oneelectric machine at the transmission input. Furthermore, this controlstrategy is applicable to conventional automatic transmission, dualclutch powershift transmissions, and converterless automatictransmissions.

The scope of applicability of the preferred embodiment will becomeapparent from the following detailed description, claims and drawings.It should be understood, that the description and specific examples,although indicating preferred embodiments of the invention, are given byway of illustration only. Various changes and modifications to thedescribed embodiments and examples will become apparent to those skilledin the art.

DESCRIPTION OF THE DRAWINGS

The invention will be more readily understood by reference to thefollowing description, taken with the accompanying drawings, in which:

FIG. 1 is a schematic diagram showing an automotive vehicle powertrainfor a hybrid electric vehicle;

FIG. 2 is a schematic diagram showing propulsion and power flow of thevehicle powertrain of FIG. 1;

FIG. 3 is a schematic diagram showing vectors representing torquetransmission among components of the powertrain operating in mode A;

FIG. 4 is a schematic diagram showing vectors representing torquetransmission among components of the powertrain operating in mode B;

FIGS. 5A-5D illustrate the change of powertrain variables during atransmission upshift performed with input torque modulation;

FIGS. 6A-6D illustrate the change of powertrain variables during atransmission downshift performed with input torque modulation;

FIG. 7 is a logic flow diagram of an algorithm for providing inputtorque modulation transmission control in the HEV powertrain of FIG. 1;

FIG. 8 is a logic flow diagram of an algorithm for selecting theoperating mode of the powertrain of FIG. 1 during input torquemodulation control; and

FIG. 9 is a schematic diagram showing vectors representing torquetransmission among components of the powertrain operating in mode C.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIGS. 1 and 2, the powertrain 10 configurationincludes a first power source such as an internal combustion engine 12,a diesel engine or a gasoline engine; a power transmission 14 producingmultiple forward and reverse gear ratios, such as a wet-clutchpowershift transmission; an electric machine 16 driveably connected tothe engine crankshaft and transmission input 18, such as acrankshaft-integrated starter/generator (CISG) for providingstarter/generator capability; and an additional electric machine 20driveably connected to a rear axle differential mechanism 36, such as anelectric rear axle drive (ERAD), for providing additional propulsioncapability in either an electric drive or hybrid drive mode. Thetransmission output 24 is connected through a final drive unit anddifferential mechanism 26 to the front axles 28, 30, which drive thefront wheels 32, 33, respectively. ERAD 20 drives the rear wheels 34, 35through ERAD gearing 48, a differential mechanism 36, rear axles 22, 23and wheels 34, 35.

The powertrain 10 comprises a first power path driveably connected tothe load that includes CISG 16, transmission 14, final drive unit 26,axles 28, 30 and the wheels 32, 33. A gear of the transmission must beengaged between input 18 and output 24 and the input clutch 38 or 39that is associated with the engaged gear must be engaged to complete adrive path between CISG 16 and the vehicle wheels 32, 33. Powertrain 10also comprises a second power path driveably connected to the load thatincludes ERAD 20, ERAD gearing 48, a differential mechanism 36, rearaxles 22, 23 and wheels 34, 35.

An electronic engine control module (ECM) 24 controls operation ofengine 12. An electronic transmission control module (TCM) 27 controlsoperation of transmission 14 and the input clutches 38, 39. Anintegrated starter controller (ISC) 40 controls operation of CISG 16,ERAD 20 and the system for charging an electric storage battery 42,which is electrically coupled to the electric machines 16, 20.

FIG. 2 shows the power and energy flow paths from the power sources 12,16, 20 to the load at the vehicle wheels 32-35. Power produced by engine12 and power produced by CISG 16 are combined at 44 and transmitted tothe transmission input 18. Electric power produced by both electricmachines 16, 20 is combinable at 46 for charging the battery 42, or istransmitted from the battery to the electric machines. Mechanical powerproduced by ERAD 20 is transmitted through ERAD gearing 48 to the loadat the rear wheels 34, 35 through the rear final drive 36.

In a hybrid electric vehicle application in which a fixed-ratiotransmission is used and at least one electric machine is coupled to theengine crankshaft 18 to provide engine start/stop capability such as acrankshaft integrated starter/generator (CISG) 16, enhanced input torquemodulation can be provided during transmission shifts in a superiormethod compared to that of a conventional input torque modulationstrategy.

As shown in FIGS. 3 and 4, operating modes of the powertrain 10 are usedto provide transmission input torque modulation during transmissionshift events. Depending on the type of shift event, i.e., an upshift ordownshift, level of torque modulation request, CISG operatingconditions, battery conditions, and other factors, the appropriatepowertrain operating mode will be used to provide the desired inputtorque modulation request. FIG. 3 is a schematic diagram of thepowertrain 10 showing vectors representing torque transmission amongcomponents during operating mode A, in which the CISG 16 reducestransmission output torque during an upshift.

FIGS. 5A-5D illustrate the change of certain powertrain variables duringa transmission upshift in which input torque modulation is provided bythe CISG 16 using operating mode A, whose power flow among powertraincomponents is illustrated in FIG. 3. In operating mode A, CISG 16operates as an electric generator to provide input torque modulation andto reduce the transmission output torque disturbance 50 that wouldresult if no torque modulation were being performed. CISG is operativefor this purpose provided that the CISG is available, i.e., its currenttemperature is less than its temperature limit, its speed is less thanits operational speed limit, etc., and the battery state of charge (SOC)is below the maximum allowable limit.

In operating mode A, CISG 16 is driven by engine 12, thereby reducingthe net torque 52 transmitted by crankshaft 18 to the input oftransmission 14 during the ratio change phase 54 of the upshift, i.e.,while the change gear ratio change 56 is occurring following the torquetransfer phase 55. The negative CISG torque 58, which is controlled toprovide input torque modulation during the shifts is shown in FIG. 5D.As shown in FIG. 5C, excess torque 60 produced by engine 12 during theratio change phase is recovered and converted into electrical energythat is stored by the battery 42, while achieving the requested inputtorque modulation and providing optimum shift quality.

FIG. 5A illustrates the difference 62 between the magnitude of torque 64at the transmission output shaft 24 with CISG 16 providing input torquemodulation for optimum shift quality and the output torque 50 with noinput torque modulation provided.

Delays in crankshaft torque reduction can be avoided by taking advantageof the responsiveness of CISG 16 thus leading to accurate input torquemodulation levels. Operating mode A can also be used with both CISG 16and engine 12 reducing the net crankshaft torque to meet the requestedinput torque modulation level. This is useful in the case where the CISGmay not be fully available for input torque modulation or the batterySOC is near its maximum limit.

FIGS. 6A-6D illustrate the change of certain powertrain variables duringa transmission downshift in which input torque modulation is provided bythe CISG 16 using both operating modes A and B, whose power flow amongpowertrain components is illustrated in FIGS. 3 and 4, respectively.

As FIG. 6A shows, during the ratio change or ratio change phase 54 ofthe downshift, powertrain 10 is placed in operating mode B as shown inFIG. 4, wherein CISG 16 operates as an electric motor to increase thetransmission output torque to a level 68 rather than a output torquedrop 76 that would result if no torque modulation were being performed.During the ratio change phase 54 of the downshift, CISG torque 70supplements the engine torque 72 so that the net crankshaft torque 74 isincreased to output shaft torque level 68 in order to offset thetransmission output torque decrease 76, which would occur without torquemodulation. This would provide acceleration continuity during thedownshift and improved shift performance.

Operating mode B is used provided that the CISG 16 is available, i.e.,its current temperature is less than its temperature limit, its speed isless than its operational speed limit, and the battery state of charge(SOC) is greater than the minimum allowable limit. This CISG capabilityis unique to that of an HEV since the CISG can be used to offset theoutput torque drop 76 so that the driver can sense accelerationcontinuity during the downshift.

During the torque transfer phase 55 near the completion of thedownshift, as shown in FIGS. 6A and 6C, powertrain 10 functions inoperating mode A with CISG 16 operating as a electric generator in orderto provide input torque modulation. As shown in FIGS. 6C and 6D, CISG 16is controlled to a negative torque 78 near the end of the downshiftduring the torque transfer phase to provide torque modulation so thatthe net crankshaft torque 74 is reduced in order to minimize oreliminate the transmission output torque spike 80, which would normallyoccur without the CISG providing torque modulation. This excesscrankshaft torque 82 produced by the engine 12 is converted toelectrical energy and stored by the battery 42, while achieving therequested input torque modulation and providing optimum shift quality.Moreover, by taking advantage of the responsiveness of CISG 16, delaysin crankshaft torque reduction can be avoided thus leading to accurateinput torque modulation control during the downshift.

FIG. 7 shows the steps of an algorithm for providing input torquemodulation transmission control of the HEV powertrain of FIG. 1. Afterexecution of the algorithm is started and the operating conditions ofpowertrain 10 are assessed at step 90, a test is performed at step 92 todetermine whether a gear ratio change of the transmission 14 has beenrequested by a transmission controller acting in response to vehicleparameters that include without limitation engine throttle position,accelerator pedal position, vehicle speed, engine speed, the position ofa manually operated gear selector, and a schedule of the preferred gearratios related to the vehicle parameters.

If the result of test 92 is logically positive, control advances to step94 where a test is performed to determine whether shift input torquemodulation is requested by the controller. If the result of either test92 or 94 is logically negative, control returns to step 90. But if theresult of test 94 is positive, the magnitude of desired input torquemodulation is determined at step 96. The desired magnitude of inputtorque modulation is determined based on the shift event progress. Forexample, at the beginning of the ratio change phase of an upshift, thedesired magnitude will ramp from zero to a negative steady-state levelas the ratio change continues and will ramp back to zero as the ratiochange phase is completed.

At step 98, the operating mode of powertrain 10 is selected inaccordance with the algorithm of FIG. 8 upon reference to currentoperating parameters and the desired magnitude of input torquemodulation.

At step 100, powertrain 10 is placed in the desired operating modeselected by the algorithm of FIG. 8 in order to provide the desiredinput torque modulation during the shift event.

Referring now to the algorithm for selecting the desired operating modeshown in FIG. 8, a test is performed at step 102 to determine whetherthe CISG temperature is less than a high temperature reference.

If the result of test 102 is positive, a test is performed at step 104to determine whether the speed of CISG 16 is less than a reference speedrepresenting the maximum allowable operating speed of the CISG.

If the result of test 104 is positive, a test is performed at step 106to determine whether the magnitude of a request for transmission inputtorque modulation is less than a reference torque limit representing thecurrent maximum torque capability of CISG 16.

If the result of any of tests 102, 104 or 106 is negative, controladvances to step 108, where powertrain 10 is placed in operating mode C,in which torque produced by engine 12 alone is transmitted totransmission output 24 without CISG torque affecting any change intorque carried on crankshaft 18 to the transmission input and CISG 16neither produces or draws power. Operating mode C, shown in FIG. 9, isthat of a conventional vehicle and the engine torque will be reduced toprovide the desired level of input torque modulation since the CISGcannot be used.

If the result of test 106 is positive, a test is performed at step 110to determine whether the desired magnitude of transmission input torquemodulation is negative. If the result of test 110 is positive indicatingthat the desired input torque modulation level is negative and thecrankshaft torque is to be reduced, a test is performed at step 112 todetermine whether the battery SOC is less than a maximum allowable SOCreference.

If the result of test 112 is positive indicating that the battery SOCcan be further increased as the CISG is operated as an electricgenerator, at step 114 operating mode A is selected, indicating thatCISG 16 is available for input torque modulation by converting powerproduced by engine 12 into electrical energy to be stored by the batteryduring an upshift or downshift while achieving the desired input torquemodulation level.

If the result of test 112 is negative indicating that the battery SOCcannot be further increased, control advances to step 108, wherepowertrain 10 is placed in operating mode C, in which torque produced byengine 12 alone is transmitted to transmission output 24 without CISGtorque affecting any change in torque carried on crankshaft 18 to thetransmission input and CISG 16 neither produces or draws power.

If the result of test 110 is negative indicating that the desired inputtorque modulation level is positive and the crankshaft torque is to beincreased, a test is performed at step 116 to determine whether thebattery SOC is greater than a minimum SOC before operating the CISG asan electric motor and discharging the battery.

If the result of test 116 is positive, at step 118 operating mode B isselected, indicating that CISG 16 is available for torque modulation bysupplementing power produced by engine 12 during a downshift.

If the result of test 116 is negative, control advances to step 108,where powertrain 10 is placed in operating mode C, in which torqueproduced by engine 12 alone is transmitted to transmission output 24without CISG torque affecting any change in torque carried on crankshaft18.

In accordance with the provisions of the patent statutes, the preferredembodiment has been described. However, it should be noted that thealternate embodiments can be practiced otherwise than as specificallyillustrated and described.

1. A method for controlling transmission input torque during an upshift,comprising: (a) using an engine to produce transmission input torque;(b) during a torque transfer phase of the upshift, maintaining anelectric machine inactive; (c) if temperature of the electric machine isless than a reference, during a ratio change phase of the upshift,operating the electric machine as a generator to reduce transmissioninput torque; and (d) storing energy produced by the electric machineduring the upshift.
 2. The method of claim 1 further comprising the stepof: discontinuing use of the electric machine if the temperature of theelectric machine is equal to or greater than the reference.
 3. Themethod of claim 1 further comprising the steps of: determining whether aspeed of the electric machine is less than a reference speed; executingstep (c) if the speed of the electric machine is less than the referencespeed; and discontinuing use of the electric machine if the speed of theelectric machine is equal to or greater than the reference speed.
 4. Themethod of claim 1 further comprising the steps of: determining whether adesired magnitude of torque modulation is less than a current torquecapability of the electric machine; executing step (c) if the desiredmagnitude of torque modulation is less than the current torquecapability of the electric machine; and discontinuing use of theelectric machine if the desired magnitude of torque modulation is equalto or greater than the current torque capability of the electricmachine.
 5. The method of claim 1 further comprising the steps of:determining whether a battery state of charge is less than a referencemaximum state of charge; executing step (c) if the battery state ofcharge is less than the reference maximum state of charge; anddiscontinuing use of the electric machine if battery state of charge isequal to or greater than the reference maximum state of charge.
 6. Amethod for controlling transmission input torque during an upshift,comprising: (a) during a torque transfer phase of the upshift,maintaining an electric machine inactive; (b) if temperature of theelectric machine is less than a reference, during a ratio change phaseof the upshift, operating an electric machine as a generator; (c) duringthe ratio change phase, controlling a net torque transmitted to thetransmission input by using the engine to drive the transmission and theelectric machine concurrently; (d) discontinuing use of the electricmachine if said temperature is greater than the reference.
 7. The methodof claim 6 further comprising the step of storing in a battery energyproduced by the electric machine during the upshift.
 8. The method ofclaim 6 wherein step (c) further comprises the step of varying amagnitude of torque required to drive the electric machine.
 9. Themethod of claim 6 further comprising the steps of: determining whether aspeed of the electric machine is less than a reference speed; executingstep (b) if the speed of the electric machine is less than the referencespeed; and discontinuing use of the electric machine if the speed of theelectric machine is equal to or greater than the reference speed. 10.The method of claim 6 further comprising the steps of: determiningwhether a desired magnitude of torque modulation is less than a currenttorque capability of the electric machine; executing step (b) if thedesired magnitude of torque modulation is less than the current torquecapability of the electric machine; and discontinuing use of theelectric machine if the desired magnitude of torque modulation is equalto or greater than the current torque capability of the electricmachine.
 11. The method of claim 6 further comprising the steps of:determining whether a battery state of charge is less than a referencemaximum state of charge; executing step (b) if the battery state ofcharge is less than the reference maximum state of charge; anddiscontinuing use of the electric machine if battery state of charge isequal to or greater than the reference maximum state of charge.
 12. Amethod for controlling transmission input torque during an upshift,comprising: (a) during a torque transfer phase of the upshift,maintaining an electric machine inactive; (b) if temperature of theelectric machine is less than a reference, during a ratio change phase,operating an electric machine as an electric generator; (c) during theratio change phase, producing variable transmission input torque usingan engine; (d) producing torque transmitted to the transmission inputusing the engine and the electric machine to drive the transmissioninput; (e) discontinuing use of the electric machine if said temperatureis greater than the reference.
 13. The method of claim 12 furthercomprising the step of storing in a battery energy produced by theelectric machine during the upshift.
 14. The method of claim 12 whereinstep (d) further comprises the step of varying a magnitude of torquerequired to drive the electric machine.
 15. The method of claim 12further comprising the steps of: determining whether a speed of theelectric machine is less than a reference speed; executing step (b) ifthe speed of the electric machine is less than the reference speed; anddiscontinuing use of the electric machine if the speed of the electricmachine is equal to or greater than the reference speed.
 16. The methodof claim 12 further comprising the steps of: determining whether adesired magnitude of torque modulation is less than a current torquecapability of the electric machine; executing step (b) if the desiredmagnitude of torque modulation is less than the current torquecapability of the electric machine; and discontinuing use of theelectric machine if the desired magnitude of torque modulation is equalto or greater than the current torque capability of the electricmachine.
 17. The method of claim 12 further comprising the steps of:determining whether a battery state of charge is less than a referencemaximum state of charge; executing step (b) if the battery state ofcharge is less than the reference maximum state of charge; anddiscontinuing use of the electric machine if battery state of charge isequal to or greater than the reference maximum state of charge.